Unlocking high-speed and high-resolution photonic-swept microwave frequency identification via the ringing effect

Achieving both a high sweep rate and a high frequency resolution simultaneously remains a long-standing challenge in photonic-swept microwave frequency identification systems based on frequency-to-time mapping (FTTM), which has hindered their adoption in fast-changing electromagnetic environments. Here, we report a ringing-enhanced FTTM system by fully exploiting the ringing effect in an ultrahigh-Q chip-scale optical ring resonator (ORR). When a high-linearity optical signal rapidly sweeps through an ORR resonance, it substantially excites strong ringing oscillations. This transient oscillatory behavior results from the storage and dissipation of optical energy within the resonator. These oscillatory signatures are subsequently converted into chirped electrical pulses and digitally processed using correlation techniques, thereby establishing a fine-grained linear FTTM. A coherent rapidly swept laser source and a hybrid ORR are developed and incorporated in an FTTM-based frequency identification system. The experimental demonstration achieves a sweep rate of 5.5 GHz/μs, outperforming state-of-the-art electrical architectures by 4 orders of magnitude, with a frequency resolution of 20.0 MHz, a measurement accuracy of ±1.0 MHz, and a potential operational bandwidth of 50.1 GHz. These results open a new route for high-throughput, high-precision microwave analysis, especially for next-generation agile radar and electronic warfare systems requiring both speed and resolution under real-time constraints.